An Auxiliary power unit (APU) is provided in aircraft to provide power to aircraft systems to either supplement or substitute power generated by the main engines. An APU is typically a small gas turbine engine that is mounted within the aircraft fuselage and draws air through inlets defined within the outer skin of the aircraft. Because the APU is mounted within the aircraft fuselage, noise control features are provided to reduce noise communicated into the aircraft cabin and around the aircraft when on the ground or in the air. The inlets are open both during flight and while on the ground.